O-rings used for vacuum sealing applications such as plasma etching reactors require appropriately designed grooves to position the O-rings against the sealing surfaces. See, for example, commonly-owned U.S. Pat. Nos. 6,010,133 and 6,536,777, the disclosures of which are hereby incorporated by reference. A single or double dove-tailed groove is typically used to position the O-ring and to prevent the O-ring from falling out during the installation process. However, when multiple small O-rings need to be placed close to each other, there might be insufficient distance to accommodate the O-ring grooves on the parts to be sealed.